Abstract:

A fuel cell system includes a fuel cell, a cathode supply passage, a
cathode discharging passage, an anode supply passage, an anode
discharging passage, a pair of cathode shutoff units, an anode shutoff
unit, an anode discharging unit, a discharged gas processing unit, and a
control unit. The control unit releases the sealing of the cathode
passage by the pair of cathode shutoff units, at the time of start-up of
the fuel cell system, and releases the sealing of the anode passage by
the anode discharging unit, thereby performing a purge process to allow
discharge of the anode gas.

Claims:

1. A fuel cell system comprising:a fuel cell including a solid polymer
electrolyte membrane, and a cathode passage and an anode passage, with
the solid polymer electrolyte membrane being interposed between the
cathode passage and the anode passage, the fuel cell supplying cathode
gas to the cathode passage and supplying anode gas to the anode passage
to generate electric power;a cathode supply passage through which the
cathode gas is supplied to the cathode passage;a cathode discharging
passage through which cathode discharged gas is discharged from the
cathode passage;an anode supply passage through which the anode gas is
supplied to the anode passage;an anode discharging passage through which
anode discharged gas is discharged from the anode passage;a pair of
cathode shutoff units each installed in the cathode supply passage and
the cathode discharging passage;an anode shutoff unit installed in the
anode supply passage;an anode discharging unit installed in the anode
discharging passage;a discharged gas processing unit installed in a
downstream side rather than the cathode shutoff unit of the cathode
discharging passage and the anode discharging unit of the anode
discharging passage; anda control unit for performing sealing of the
cathode passage by the pair of cathode shutoff units and simultaneously
performing sealing of the anode passage by the anode shutoff unit and the
anode discharging unit, at the time of stoppage of electric power
generation of the fuel cell,wherein the control unit releases the sealing
of the cathode passage by the pair of cathode shutoff units, at the time
of start-up of the fuel cell system, and then releases the sealing of the
anode passage by the anode discharging unit, thereby performing a purge
process to allow discharge of the anode gas.

2. The fuel cell system according to claim 1, further comprising:anode
gas-quantity acquiring unit for acquiring a quantity of the anode gas
existing in the cathode passage,wherein the control unit calculates a
time until the purge process is allowed after the sealing of the cathode
passage by the pair of cathode shutoff units is released, based on the
quantity of the anode gas acquired by the anode gas-quantity acquiring
unit.

3. The fuel cell system according to claim 2, wherein the anode
gas-quantity acquiring unit estimates that as a soak time from the
stoppage of the electric power generation of the fuel cell to restart of
the fuel cell system is prolonged, the quantity of the anode gas existing
in the cathode passage is large.

4. The fuel cell system according to claim 2, wherein the anode
gas-quantity acquiring unit is an anode gas sensor installed in the
cathode passage.

5. The fuel cell system according to claim 1, wherein at the time of
restart of the fuel cell system, the control unit (i) releases the
sealing of the cathode passage by the pair of cathode shutoff units to
start to supply the cathode gas to the cathode passage, simultaneously,
(ii) releases the sealing of the anode passage by the anode shutoff unit
to start to supply the anode gas to the anode passage, and (iii) in the
case in which electric power generating voltage displaying performance of
the fuel cell generating the electric power is equal to or more than a
predetermined voltage, allows an electric current to be extracted from
the fuel cell.

6. The fuel cell system according to claim 5, wherein the control unit
restricts extraction of an electric current from the fuel cell, before
the electric power generating voltage of the fuel cell is equal to or
more than the predetermined voltage.

7. A method of starting a fuel cell system including:a fuel cell including
a solid polymer electrolyte membrane, and a cathode passage and an anode
passage, with the solid polymer electrolyte membrane being interposed
between the cathode passage and the anode passage, the fuel cell
supplying cathode gas to the cathode passage and supplying anode gas to
the anode passage to generate electric power;a cathode supply passage
through which the cathode gas is supplied to the cathode passage;a
cathode discharging passage through which cathode discharged gas is
discharged from the cathode passage;an anode supply passage through which
the anode gas is supplied to the anode passage;an anode discharging
passage through which anode discharged gas is discharged from the anode
passage;a pair of cathode shutoff units each installed in the cathode
supply passage and the cathode discharging passage;an anode shutoff unit
installed in the anode supply passage;an anode discharging unit installed
in the anode discharging passage;a discharged gas processing unit
installed in a downstream side rather than the cathode shutoff unit of
the cathode discharging passage and the anode discharging unit of the
anode discharging passage; anda control unit for performing sealing of
the cathode passage by the pair of cathode shutoff units and
simultaneously performing sealing of the anode passage by the anode
shutoff unit and the anode discharging unit, at the time of stoppage of
electric power generation of the fuel cell,wherein the control unit
releases the sealing of the cathode passage by the pair of cathode
shutoff units, at the time of start-up of the fuel cell system, and
releases the sealing of the anode passage by the anode discharging unit,
thereby performing a purge process to allow discharge of the anode gas.

Description:

BACKGROUND OF THE INVENTION

[0001]Priority is claimed on Japanese Patent Application No. 2008-320771,
filed on Dec. 17, 2008, the contents of which are incorporated herein by
reference.

FIELD OF THE INVENTION

[0002]The present invention relates to a fuel cell system and a method of
starting the fuel cell system.

DESCRIPTION OF THE RELATED ART

[0003]A fuel cell has been developed, in which a solid polymer electrolyte
membrane is interposed to form a cathode passage and an anode passage,
and cathode gas is supplied to the cathode passage, while anode gas is
supplied to the anode passage, thereby generating electric power. A fuel
cell system having such a kind of fuel cell includes a cathode supply
passage for supplying the cathode gas to the cathode passage, a cathode
discharging passage for discharging cathode discharged gas from the
cathode passage, an anode supply passage for supplying the anode gas to
the anode passage, and an anode discharging passage for discharging anode
discharged gas from the anode passage. Also, a diluting system for
diluting the anode gas with the cathode gas is installed at a downstream
side of the cathode discharging passage and the anode discharging
passage.

[0004]Also, the fuel cell system further includes a shutoff valve disposed
in the anode supply passage and a purge valve disposed in the anode
discharging passage. At the time of stoppage of the electric power
generation of the fuel cell, sealing of the anode passage is performed by
closing the shutoff valve and the purge valve. In this instance, while a
finite quantity of the anode gas is sealed off in the anode passage, an
infinite quantity of the cathode gas exists in the cathode passage. As a
result, there is concern that unexpected reaction may occur to
deteriorate the solid polymer electrolyte membrane. Accordingly, a
technique for performing the sealing of the cathode passage by installing
a sealing valve in the cathode gas supply passage and the cathode
discharging passage, respectively, and closing the pair of sealing valves
at the time of stoppage of the electric power generation of the fuel cell
has been proposed (e.g., see Japanese Unexamined Patent Application,
First Publication No. 2005-93115).

[0005]Meanwhile, at the time of start-up of the fuel cell system, the pair
of sealing valves is opened to release the sealing of the cathode
passage, thereby performing cathode recovery process which supplies the
cathode gas to the cathode passage.

[0006]Further, at the time of start-up of the fuel cell system, OCV (Open
Circuit Voltage) purge process (hereinafter referred to as a purge
process) is performed. This process firstly releases the sealing of the
anode passage by the shutoff valve. Next, the anode gas is supplied to
the anode passage to increase the pressure of the anode passage. Then,
the sealing of the anode passage by the purge valve is released to allow
the anode gas to be discharged. The purge process is carried out so that
impure gas remaining in the anode passage may be discharged to replenish
the anode passage with the high-concentration anode gas.

[0007]If the purge is performed, the anode gas filled in the anode passage
is discharged, and then is supplied to the diluting system.

[0008]During the stoppage of the electric power generation of the fuel
cell, however, the anode gas sealed off in the anode passage permeates
the solid polymer electrolyte membrane and thus leaks to the cathode
passage. As a result, the anode gas exists also in the cathode passage at
the time of start-up of the fuel cell system. If the cathode recovery
process is performed in this state, the anode gas existing in the cathode
passage is discharged, and then is supplied to the diluting system.
Consequently, there is a problem in that if the purge process and the
cathode recovery process are simultaneously performed, a lot of anode gas
is supplied to the diluting system, and thus the diluting system
overflows, so that the diluting is not sufficiently carried out.

SUMMARY OF THE INVENTION

[0009]Therefore, an object of the invention is to provide a fuel cell
system and a method of starting the fuel cell system, which can prevent
overflow of a discharged gas processing unit at the time of start-up of
the fuel cell system.

[0010](1) A fuel cell system according to the invention includes a fuel
cell having a solid polymer electrolyte membrane, and a cathode passage
and an anode passage, with the solid polymer electrolyte membrane being
interposed between the cathode passage and the anode passage, the fuel
cell supplying cathode gas to the cathode passage and supplying anode gas
to the anode passage to generate electric power; a cathode supply passage
through which the cathode gas is supplied to the cathode passage; a
cathode discharging passage through which cathode discharged gas is
discharged from the cathode passage; an anode supply passage through
which the anode gas is supplied to the anode passage; an anode
discharging passage through which anode discharged gas is discharged from
the anode passage; a pair of cathode shutoff units each installed in the
cathode supply passage and the cathode discharging passage; an anode
shutoff unit installed in the anode supply passage; an anode discharging
unit installed in the anode discharging passage; a discharged gas
processing unit installed in a downstream side rather than the cathode
shutoff unit of the cathode discharging passage and the anode discharging
unit of the anode discharging passage; and a control unit for performing
sealing of the cathode passage by the pair of cathode shutoff units and
simultaneously performing sealing of the anode passage by the anode
shutoff unit and the anode discharging unit, at the time of stoppage of
electric power generation of the fuel cell, wherein the control unit
releases the sealing of the cathode passage by the pair of cathode
shutoff units, at the time of start-up of the fuel cell system, and then
releases the sealing of the anode passage by the anode discharging unit,
thereby performing a purge process to allow discharge of the anode gas.

[0011]With the fuel cell system according to (1) above, the sealing of the
cathode passage is released, and the anode gas in the cathode passage is
supplied to and processed in the discharged gas processing unit. And
then, the sealing of the anode passage is released, and then the anode
gas in the anode passage is supplied to and processed in the discharged
gas processing unit. As a result, it is possible to process the anode gas
in the discharged gas processing unit little by little, thereby
preventing overflow of the anode gas in the discharged gas processing
unit.

[0012](2) The fuel cell system according to (1) above may further include
anode gas-quantity acquiring unit for acquiring a quantity of the anode
gas existing in the cathode passage, wherein the control unit calculates
a time until the purge process is allowed after the sealing of the
cathode passage by the pair of cathode shutoff units is released, based
on the quantity of the anode gas acquired by the anode gas-quantity
acquiring unit.

[0013]With the fuel cell system according to (2) above, after the quantity
of the anode gas in the cathode passage is decreased, the purge process
can be performed. As a result, it is possible to prevent the situation in
which the purge process is performed while the discharge of the anode gas
in the cathode passage continues, thereby preventing the overflow of the
anode gas in the discharged gas processing unit. Also, it is possible to
prevent the situation in which the purge process is not performed
although the discharge of the anode gas in the cathode passage is
completed, thereby quickly starting the fuel cell system.

[0014](3) In the fuel cell system according to (2) above, the anode
gas-quantity acquiring unit may estimate that as a soak time from the
stoppage of the electric power generation of the fuel cell to restart of
the fuel cell system is prolonged, the quantity of the anode gas existing
in the cathode passage is large.

[0015]With the fuel cell system according to (3) above, as a soak time is
prolonged, the quantity of the anode gas permeating the solid polymer
electrolyte membrane from the anode passage and leaking to the cathode
passage is increased, so that the quantity of the anode gas existing in
the cathode passage can be accurately seized.

[0016](4) In the fuel cell system according to (2) above, the anode
gas-quantity acquiring unit may be an anode gas sensor installed in the
cathode passage.

[0017]With the fuel cell system according to (4) above, since the
detection is performed by the anode gas sensor, the quantity of the anode
gas existing in the cathode passage can be accurately seized.

[0018](5) In the fuel cell system according to any one of (1) to (4)
above, at the time of restart of the fuel cell system, the control unit
may (i) release the sealing of the cathode passage by the pair of cathode
shutoff units to start to supply the cathode gas to the cathode passage,
simultaneously, (ii) release the sealing of the anode passage by the
anode shutoff unit to start to supply the anode gas to the anode passage,
and (iii) in the case in which electric power generating voltage
displaying performance of the fuel cell generating the electric power is
equal to or more than a predetermined voltage, allow an electric current
to be extracted from the fuel cell.

[0019]With the fuel cell system according to (5) above, before the purge
process is completed, the electric power generated by the fuel cell can
be used without waste.

[0020](6) In the fuel cell system according to (5) above, the control unit
may restrict extraction of an electric current from the fuel cell, before
the electric power generating voltage of the fuel cell is equal to or
more than the predetermined voltage.

[0021]With the fuel cell system according to (6) above, it is possible to
prevent deterioration of the solid polymer electrolyte membrane by
generating the electric power before the purge process is completed.

[0022](7) In a method of starting a fuel cell system according to the
invention, the fuel cell system including a fuel cell having a solid
polymer electrolyte membrane, and a cathode passage and an anode passage,
with the solid polymer electrolyte membrane being interposed between the
cathode passage and the anode passage, the fuel cell supplying cathode
gas to the cathode passage and supplying anode gas to the anode passage
to generate electric power; a cathode supply passage through which the
cathode gas is supplied to the cathode passage; a cathode discharging
passage through which cathode discharged gas is discharged from the
cathode passage; an anode supply passage through which the anode gas is
supplied to the anode passage; an anode discharging passage through which
anode discharged gas is discharged from the anode passage; a pair of
cathode shutoff units each installed in the cathode supply passage and
the cathode discharging passage; an anode shutoff unit installed in the
anode supply passage; an anode discharging unit installed in the anode
discharging passage; a discharged gas processing unit installed in a
downstream side rather than the cathode shutoff unit of the cathode
discharging passage and the anode discharging unit of the anode
discharging passage; and a control unit for performing sealing of the
cathode passage by the pair of cathode shutoff units and simultaneously
performing sealing of the anode passage by the anode shutoff unit and the
anode discharging unit, at the time of stoppage of electric power
generation of the fuel cell, the control unit releases the sealing of the
cathode passage by the pair of cathode shutoff units, at the time of
start-up of the fuel cell system, and then releases the sealing of the
anode passage by the anode discharging unit, thereby performing a purge
process to allow discharge of the anode gas.

[0023]With the method of starting the fuel cell system according to (7)
above, the sealing of the cathode passage is released, and the anode gas
in the cathode passage is supplied to and processed in the discharged gas
processing unit. And then, the sealing of the anode passage is released,
and then the anode gas in the anode passage is supplied to and processed
in the discharged gas processing unit. As a result, it is possible to
process the anode gas in the discharged gas processing unit little by
little, thereby preventing the overflow of the anode gas in the
discharged gas processing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a block diagram schematically showing the configuration of
a fuel cell system according to an embodiment of the invention.

[0025]FIG. 2 is a flowchart showing a method of starting a fuel cell
system according to an embodiment of the invention.

[0026]FIG. 3 is a graph depicting a relation between a soak time and a
quantity of anode gas existing in a cathode passage.

[0027]FIG. 4 is a graph depicting a relation between a quantity of anode
gas in a cathode passage and a purge allowing time.

[0028]FIG. 5 is a timing chart depicting a method of starting a fuel cell
system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029]Embodiments of the invention will now be described with reference to
the accompanying drawings. In this embodiment, a fuel cell system
equipped in an electrical vehicle is described as an example.

[0030](Fuel Cell System)

[0031]FIG. 1 is a block diagram schematically showing the configuration of
a fuel cell system 1 according to an embodiment of the invention.

[0032]The fuel cell system 1 includes a fuel cell 10 for generating
electric power by supplying cathode gas and anode gas. The fuel cell 10
has a plurality of unit fuel cells (hereinafter referred to as "a unit
cell") which are stacked and electrically connected in series to each
other. The unit cell is formed by disposing separators at both sides of a
membrane electrode structure. The member electrode structure is
constituted by an anode electrode and a cathode electrode which are
disposed at both sides of a solid polymer electrolyte membrane
(electrolyte membrane) made of, for example, a fluorine-based electrolyte
material. The anode-side separator is disposed with facing to the anode
electrode of the membrane electrode structure, and an anode passage 25 is
formed between the anode-side separator and the anode electrode. Also, a
cathode-side separator is disposed with facing to the cathode electrode
of the membrane electrode structure, and a cathode passage 35 is formed
between the cathode-side separator and the cathode electrode.

[0033]In the fuel cell 10, the anode passage 25 is supplied with fuel gas,
such as hydrogen gas, as the anode gas, and the cathode passage 35 is
supplied with an oxidizer gas, such as air containing oxygen, as the
cathode gas. As a result, hydrogen ion generated from the anode electrode
by catalytic reaction transfers to the cathode electrode through the
solid polymer electrolyte membrane. The hydrogen ion causes an
electrochemical reaction with oxygen at the cathode electrode to generate
the electric power. In addition, the fuel cell 10 is provided with a
voltmeter 12.

[0034]An inlet side of the anode passage 25 is connected to a hydrogen
supply system 22 and an anode supply passage 23 for supplying the anode
gas to the anode passage 25. The anode supply passage 23 is provided with
a shutoff valve (anode shutoff unit) for blocking the supply of the anode
gas.

[0035]Further, an outlet side of the anode passage 25 is connected to an
anode discharging passage 27 for discharging anode discharged gas from
the anode passage 25. The anode discharging passage 27 is provided with a
purge valve (anode discharging unit) for purging inner gas of the anode
passage 25.

[0036]Meanwhile, the inlet side of the cathode passage 35 is connected to
an air pump 32 and a cathode supply passage 33 for supplying the cathode
gas to the cathode passage 35. The cathode supply passage 33 is provided
with an inlet-side sealing valve (cathode shutoff unit) for sealing the
inlet side of the cathode passage 35.

[0037]Also, the outlet side of the cathode passage 35 is connected to the
cathode discharging passage 37 for discharging cathode discharged gas
from the cathode passage 35. The cathode discharging passage 37 is
provided with an outlet-side sealing valve (cathode shutoff unit) for
sealing the outlet side of the cathode passage 35.

[0038]The anode discharging passage 27 and the cathode discharging passage
37 are provided with a diluting system (discharged gas processing unit)
40 at the downstream side thereof. The diluting system 40 dilutes the
fuel gas with the oxidizer gas, and discharges the gas to the outside of
the fuel cell system 1. In this instance, a catalytic combustor may be
installed in place of the diluting system 40.

[0039]The diluting system 40 is provided with a hydrogen sensor 42 for
detecting concentration of exhausted hydrogen at the downstream side
thereof.

[0040]The fuel cell system 1 includes a control unit 50. The control unit
controls the opening and closing operation of the pair of sealing valves
34 and 38, the shutoff valve 24, and the purge valve 28. Also, the
control unit 50 monitors the voltmeter 12 to control the operation of the
hydrogen supply system 22 and the air pump 32.

[0041]At the time of stoppage of the electric power generation of the fuel
cell 10, the control unit 50 closes the shutoff valve 24 and the purge
valve 28 to perform the anode sealing process which seals the anode
passage 25, and simultaneously, closes the pair of sealing valves 34 and
38 to perform the cathode sealing process which seals the cathode passage
35. It is possible to prevent the unreacted anode gas from flowing
outwardly via the anode supply passage 23 or the anode discharging
passage 27 by performing the anode sealing process. In this instance, if
a finite quantity of the anode gas is filled in the anode passage 25,
while an infinite quantity of the cathode gas exists in the cathode
passage 35, there is concern in that unexpected reaction may occur to
deteriorate the solid polymer electrolyte membrane.

[0042]Accordingly, it is possible to seal the finite quantity of the
cathode gas in the cathode passage 35 by performing the cathode sealing
process, thereby preventing deterioration of the solid polymer
electrolyte membrane.

[0043]During the stop of the fuel cell 10, however, the anode gas sealed
off in the anode passage 25 permeates the solid polymer electrolyte
membrane and thus leaks to the cathode passage 35. In this embodiment, it
is possible to prevent the anode gas leaking to the cathode passage 35
from flowing outwardly via the cathode supply passage 33 or the cathode
discharging passage 37 by performing the cathode sealing process.
However, at the time of restart of the fuel cell, the anode gas exists in
the cathode passage 35. Consequently, at the time of start-up of the fuel
cell system 1, the control unit 50 opens the pair of sealing valves 34
and 38 to release the sealing of the cathode passage 35, and then
performs the cathode recovery process which supplies the cathode gas to
the cathode passage 35. The anode gas existing in the cathode passage 35
is discharged by the cathode recovery process, and then is supplied to
the diluting system 40. In this instance, in the case in which a lot of
the anode gas exists in the cathode passage 35, the pair of sealing
valves 34 and 38 is intermittently opened to discharge the anode gas to
the diluting system 40 little by little.

[0044]Also, the control unit 50 performs an OCV purge process (hereinafter
referred to as a purge process) at the time of start-up of the fuel cell
system 1. This process releases the sealing of the anode passage 25 by
the shutoff valve 24. Next, the anode passage 25 is supplied with the
anode gas to increase the pressure of the anode passage 25. And then, the
sealing of the anode passage 25 by the purge valve 28 is released to
allow the anode gas to be discharged. The impurity gas remaining in the
anode passage 25 is discharged by performing the purge process to
replenish the anode passage 25 with the high-concentration anode gas. The
anode gas existing in the anode passage 25 is discharged by the purge
process, and then is supplied to the diluting system 40. In this
instance, in the case in which a lot of anode gas exists in the anode
passage 25, the purge valve 28 is intermittently opened to discharge the
anode gas to the diluting system 40 little by little.

[0045]However, there is concern in that if the cathode recovery process
and the purge process are simultaneously performed, a lot of anode gas is
supplied to the diluting system 40, and thus the diluting system 40
overflows, so that the diluting is not sufficiently carried out.

[0046]Consequently, the control unit 50 performs the purge process after
the cathode recovery process is performed. As a result, it is possible to
prevent the overflow of the diluting system 40.

[0047]The time (purge allowing time) from the beginning of the cathode
recovery process to the allowing of the purge process is varied depending
upon a quantity of the anode gas existing in the cathode passage 35.
Consequently, the control unit 50 is provided with an anode gas-quantity
acquiring unit (not shown). In this instance, the quantity of the anode
gas leaking from the anode passage 25 to the cathode passage 35 is varied
by a soak time until ignition of the electrical vehicle is switched from
OFF to ON. As a result, the anode gas-quantity acquiring unit estimates
the quantity of the anode gas based on the soak time. In this instance,
the quantity of the anode gas may be directly detected by the anode gas
sensor disposed in the cathode passage 35.

[0048]The control unit 50 calculates the purge allowing time based on the
quantity of the anode gas acquired by the anode gas-quantity acquiring
unit.

[0049](Method of Starting Fuel Cell System)

[0050]A method of starting the fuel cell system 1 according to the
embodiment will now be described in detail.

[0051]FIG. 2 is a flowchart showing the method of starting the fuel cell
system 1 according to an embodiment of the invention, and FIG. 5 is a
timing chart.

[0052]First, at step S10 (t1 of FIG. 5), the pair of sealing valves 34 and
38 are opened.

[0053]Also, at step S12 (t1 of FIG. 5), the shutoff valve 24 is opened to
supply the anode gas from the hydrogen supply system 22 to the anode
passage 25, thereby increasing the pressure of the anode passage 25.

[0054]Next, as step S14 (t2 of FIG. 5), the air pump 32 is operated to
start to supply the cathode gas to the cathode passage 35 (cathode
recovery process). Also, in the case in which the anode supply passage 23
is provided with a regulator rendering the pressure of the cathode supply
passage 33 as signal pressure, the anode passage 25 is supplied with the
anode gas at this time.

[0055]If the cathode passage 35 is supplied with the cathode gas, the
anode gas existing in the cathode passage 35 is discharged, and then is
supplied to the diluting system 40. The diluting system 40 dilutes the
anode gas with the cathode gas to discharge it outwardly. As shown in
FIG. 5, the concentration of the hydrogen exhausted from the diluting
system 40 is increased from the operation start time t2 of the air pump
32.

[0056]In this embodiment, after the cathode recovery process is carried
out, the purge process is performed to prevent the overflow of the
diluting system 40. The detailed order will now be described in detail
hereinafter.

[0057]First, at step S16, it is determined whether or not scavenging of
the anode passage 25 and the cathode passage 35 is performed while the
electric power generation of the fuel cell 10 is stopped. If the
scavenging is performed, since the quantity of the anode gas remaining in
the anode passage 25 and the cathode passage 35 is small, it is not
necessary to take the overflow of the diluting system 40 into
consideration. In this instance, it proceeds to step S26 to perform the
purge process immediately. If the judgment of step S16 is NO, it proceeds
to step S18.

[0058]Next, at step S18, the time (purge allowing time) from the beginning
of the cathode recovery process to the allowing of the purge process is
calculated. The purge allowing time is a time until the discharge of the
anode gas existing in the cathode passage 35 is almost completed, and is
determined depending upon the quantity of the anode gas in the cathode
passage 35. The quantity of the anode gas in the cathode passage is
calculated depending upon the soak time until the ignition of the
electrical vehicle is switched from OFF to ON.

[0059]FIG. 3 is a graph depicting a relation between the soak time and the
quantity of the anode gas existing in the cathode passage. As the soak
time is prolonged, the quantity of the anode gas permeating the solid
polymer electrolyte membrane from the anode passage 25 and leaking to the
cathode passage 35 is increased. As a result, in the graph A, as the soak
time is prolonged, the quantity of the anode gas is increased. If the
soak time is too prolonged, the concentration of the anode gas in both
passages 25 and 35 is equalized, and thus the leak of the anode gas is
stopped. Consequently, the quantity of the anode gas is constant in the
graph A'. Also, if the temperature during the soak is high, the leak of
the anode gas is accelerated, so that the quantity of the anode gas in
the graph B is larger than that of the anode gas in the graph A. By
contrast, if the temperature during the soak is low, the leak of the
anode gas is suppressed, so that the quantity of the anode gas in the
graph C is smaller than that of the anode gas in the graph A.

[0060]The anode gas-quantity acquiring unit estimates the quantity of the
anode gas in the cathode passage 35 based on the soak time by using the
respective graphs of FIG. 3 as a map.

[0061]FIG. 4 is a graph depicting a relation between the quantity of the
anode gas in the cathode passage and the purge allowing time. If the
quantity of the anode gas in the cathode passage is large, since it is
necessary to supply the anode gas to the diluting system 40 little by
little by intermittently opening the pair of sealing valves 34 and 38,
the time needed for the cathode recovery process is prolonged.
Consequently, the purge allowing time is extended in proportion to the
quantity of the anode gas.

[0062]The control unit 50 calculates the purge allowing time based on the
quantity of the anode gas acquired by the anode gas-quantity acquiring
unit and the graph of FIG. 4. That is, as the soak time is prolonged, the
purge allowing time is set to be long.

[0063]However, since the cathode gas flows in the cathode passage 35 by
the start of the operation of the air pump 32, and the anode gas exists
in the anode passage 25 by the opening of the shutoff valve 24, the
voltage of the fuel cell 10 is increased from the operation start time t2
of the air pump 32 in FIG. 5. That is, the fuel cell 10 is in the state
of generating the electric power, although it is limited.

[0064]Accordingly, at step S20, it is determined whether or not the
voltage of the fuel cell 10 is more than a predetermined voltage. The
predetermined voltage is set as a voltage to drive the vehicle at a slow
speed, a voltage to operate an air conditioner or the like. If the
judgment at step S20 is YES, the electric power generation is allowed at
step S22 (t3 of FIG. 5). Consequently, it is possible to use the electric
power generated by the fuel cell 10 without waste.

[0065]Since the purge valve 28 is closed at this time, the anode gas does
not flow in the anode passage 25. As a result, if the fuel cell 10 is
allowed to generate a rated electric power at this time, there is concern
in that the solid polymer electrolyte membrane may be deteriorated.
Therefore, until the purge process is completed (between t3 and t5 in
FIG. 5), extraction of the electric current from the fuel cell 10 is
restricted to a predetermined current and less. Consequently, it is
possible to prevent deterioration of the solid polymer electrolyte
membrane.

[0066]Next, at step S24, it is determined whether or not the purge
allowing time has been lapsed after the cathode recovery process starts.
If the judgment at step S24 is NO, the cathode recovery process is
continuously performed. If the judgment is YES, it proceeds to step S26.

[0067]And then, at step S26 (t4 of FIG. 5), the purge valve 28 is opened
to start the purge process. In this instance, in the case in which the
upper limit of the purge allowing time is set and then the time after the
cathode recovery process starts reaches the upper limit, the purge
process may automatically start.

[0068]In FIG. 5, a period from t2 to t4 corresponds to the purge allowing
time. The concentration of the hydrogen exhausted from the diluting
system 40 starts to increase from the start time t2 of the cathode
recovery process, and then reaches the peak. As the cathode recovery
process comes close to the completion, the concentration decreases. Next,
the concentration starts to increase again from the start time t4 of the
purge process.

[0069]Next, at step S28, it is determined whether or not the voltage of
the fuel cell 10 is more than a predetermined value (predetermined
voltage). If the judgment at step S28 is NO, the purge process is
repeated. That is, the purge valve 28 is again closed to increase the
pressure of the anode passage 25, and then the purge valve 28 is opened
to discharge the anode gas. If the judgment at step S28 is YES, it
proceeds to step S30.

[0070]And then, at step S30 (t5 of FIG. 5), the fuel cell 10 is allowed to
generate the rated electric power. In this instance, in the case in which
the upper limit of the times of the purge processes has been set and then
the times of the purge processes reaches the upper limit, the generation
of the rated electric power may be automatically allowed irrespective of
the voltage of the fuel cell 10.

[0071]The start-up of the fuel cell system 1 is completed by the above.

[0072]As concretely described above, the fuel cell system 1 according to
the embodiment is adapted to perform the purge process in which at the
time of start-up of the fuel cell system, after the sealing of the
cathode passage 35 by the pair of sealing valves 34 and 38 is released,
the sealing of the anode passage 25 by the purge valve 28 is released to
allow the anode gas to be discharged.

[0073]With the above configuration, the sealing of the cathode passage 35
is released, and the anode gas in the cathode passage 35 is supplied to
and processed in the diluting system 40. And then, the sealing of the
anode passage 25 is released, and then the anode gas in the anode passage
25 is supplied to and processed in the diluting system 40. As a result,
it is possible to process the anode gas in the diluting system 40 little
by little, thereby preventing the overflow of the diluting system 40.

[0074]Further, the fuel cell system 1 according to the embodiment includes
the anode gas-quantity acquiring unit for acquiring the quantity of the
anode gas existing in the cathode passage 35, and is adapted to calculate
the purge allowing time until the purge process is allowed after the
sealing of the cathode passage 35 by the pair of sealing valves 34 and 38
is released, based on the quantity of the anode gas acquired by the anode
gas-quantity acquiring unit.

[0075]With the configuration, after the quantity of the anode gas in the
cathode passage 35 is decreased, the purge process can be performed. As a
result, it is possible to prevent the situation in which the purge
process is performed while the discharge of the anode gas in the cathode
passage 35 continues, thereby preventing the overflow of the diluting
system 40. Also, it is possible to prevent the situation in which the
purge process is not performed although the discharge of the anode gas in
the cathode passage 35 is completed, thereby quickly starting the fuel
cell system 1.

[0076]While preferred embodiment of the invention has been described and
illustrated above, it should be understood that this is an exemplary of
the invention and is not to be considered as limiting. Additions,
omissions, substitutions, and other modifications can be made without
departing from the spirit or scope of the present invention. Accordingly,
the invention is not to be considered as being limited by the foregoing
description, and is only limited by the scope of the appended claims.

[0077]For example, the embodiment is explained by taking an example of the
fuel cell system equipped in the electric vehicle, the fuel cell system
of the invention may be applied to others besides the electric vehicle.

[0078]Also, the fuel cell system shown in FIG. 1 is an example, and may
employ other configuration.